1. Field of the Invention
The present invention relates to a quality evaluation apparatus for fruits and vegetables comprising a light emitting section for emitting light to fruits or vegetables acting as measured objects placed in a position for measurement, a light receiving section for receiving transmitted light or reflected light from the measured objects at a photo-detective sensor of charge storage type to obtain photo-detective information for quality evaluation, a transporting device for transporting the measured objects via the position for measurement, and a control device for obtaining inner quality information of the measured objects based on the photo-detective information from the light receiving section and for controlling operation of the respective sections.
Further, the present invention relates to the quality evaluation apparatus further comprising a computing section for obtaining a quality evaluation value for fruits or vegetables based on photo-detective information from the light receiving section and a calibration formula established in advance for quality evaluation for fruits and vegetables. This computing section is switchable between a state for executing a quality evaluation process of the measured objects, and a state for executing a wavelength calibration process to determine wavelengths of the light received by the light receiving section based on the photo-detective information when a reference object for wavelength calibration is measured which has a light transmission characteristic with respect to near-infrared light of specific wavelengths.
2. Description of Related Art
The quality evaluation apparatus noted above is for measuring the quality of fruits and vegetables such as oranges and apples as the measured objects, for example, including the inner quality like a sugar content, acid degree or the like, in a non-destructive condition. The conventional apparatus has the following construction.
One example of the conventional apparatus carries out a discharging operation twice for releasing charges stored in the photo-detective sensor when a measured object which is transported by the transporting device reaches a position slightly upstream of the position for measurement in a transporting direction, and more particularly when the forward end in the transporting direction of a measured object reaches a light passage point through which the light emitted from the light emitting section passes toward the light receiving section. In such an apparatus, a measurement charge storage process is executed for storing charges in the photo-detective sensor until a charge storage time as a predetermined measurement time elapses when a measured object reaches the position for measurement after the discharging operation is completed. Here, the stored charges are fetched and used as the photo-detective information for quality evaluation, thereby to obtain the inner quality information of the measured objects. In a condition where the forward end in the transporting direction of a measured object does not reach the light passage point, the photo-detective sensor continuously executes the charge storage process while a shutter mechanism is maintained in a closed state to prevent the light from entering the photo-detective sensor from outside. (See Patent Document 1, for example)
According to the above construction, the discharging operation is carried out prior to the measurement charge storage process when a measured object which is transported by the transporting device reaches the position slightly upstream of the position for measurement in the transporting direction. This prevents residual charges from remaining in the photo-detective sensor as much as possible. The photo-detective sensor receives transmitted light or reflected light from the measured object to store charges. However, part of the stored charges sometimes remain within the photo-detective sensor even after a process for fetching the stored charges. When the transmitted light or reflected light is further received from the measured objects with the residual charges being present, there occur errors in the photo-detective information, which in turn cause errors in the inner quality information of the measured objects based on the photo-detective information of the photo-detective sensor. Thus, the discharging operation is carried out prior to the measurement charge storage process, thereby to prevent the residual charges from remaining as much as possible.
With the above conventional construction, the measurement process can be executed while preventing the residual charges from remaining as much as possible when a plurality of measured objects which are transported by the transporting device successively reach the position for measurement at short time intervals. However, when the time intervals at which the measured objects are transported are irregular and become prolonged for the measured objects to be transported to the position for measurement, there is a risk of increasing the charges to be stored since the photo-detective sensor continuously executes the charge storage process unless the forward ends in the transporting direction of the measured objects reach the light passage point.
As noted above, the shutter mechanism is in the closed state to prevent the light from entering the photo-detective sensor from outside unless the forward ends in the transporting direction of the measured objects reach the light passage point. However, dark currents are generated in the photo-detective sensor in such an aphotic condition. If such dark currents are stored for a long time, stored charges are increased, which could cause saturation.
Further, it is required in the above-noted conventional construction to execute the discharging operation within a short period of time after the forward end in the transporting direction of a measured object reaches the light passage point and before the measurement charge storage process is executed. However, it is difficult to effect the discharging operation satisfactorily when saturation occurs as noted above, and residual charges sometimes remain. If it is attempted to obtain the inner quality information of the measured object based on the detected information from the photo-detective sensor under such a condition, there is a chance of causing errors in the inner quality information.
In another example of the conventional apparatus, near-infrared light is emitted to the measured objects from the light emitting section. The light transmitted through the measured objects is separated into rays by a spectroscopic device such as a concave diffraction grating. Subsequently, a photo-detective section detects the rays with wavelengths in the range of 700 nm through 1000 nm among the separated rays. The photo-detective section comprises a photodetector of the array type including a linear CCD line sensor of 1024 bits, i.e. 1024 unit photodetectors. Spectral data is obtained based on the detected information from the photodetectors and put to a quadratic differentiation to obtain second derivative spectral data. An amount of specific component contained in the measured objects is obtained using the second derivative spectral data and a calibration formula established in advance, thereby to measure the inner quality.
In this apparatus, a wavelength calibration process is executed in the following manner. This process utilizes a calibration filter as a reference object for wavelength calibration which reaches peaks in the amount of transmitted light with a pair of specific wavelengths. The photodetector of the array type receives light transmitted through the calibration filter. With reference to a positional relationship between the pair of specific wavelengths and elements (unit photodetectors) receiving the pair of peak wavelengths, each element (unit photodetector) constituting the photodetector of the array type is related to the wavelength of light received by each element. (See Patent Document 2)
Incidentally, the above calibration formula is individually established in advance for each apparatus based on data obtained from an actual measurement of samples similar to the measured objects prior to a measuring process for the measured objects. Although the prior patent documents do not describe how to establish the calibration formula in detail, it has generally been established as follows.
Tens or hundreds of measured objects are prepared as samples to obtain spectral data for each sample using a quality evaluation apparatus. Further, for each sample, a detection process is executed for accurately detecting amounts of chemical components of the measured objects by a special inspection device based on a destructive analysis, for example, thereby to obtain actual component amounts in the measured objects. Then, the spectral data obtained from each sample as noted above, and more particularly photo-detective data for all the elements of the photo-detective photodetector of the array type is used and compared with the detected results of the actual component amounts while the calibration formula is established for representing a relationship between the spectral data and the amount of the specific components by using the multiple regression analysis technique.
Thus, the photo-detective information is conventionally utilized which is obtained at the plural unit photodetectors with the same resolution in executing the wavelength calibration process and in establishing the calibration formula.
With the above-noted arrangement, since the wavelength resolution used in executing the wavelength calibration process is sufficiently small, it is possible to reduce errors in the wavelength in the photo-detective information measured by each unit photodetector when transmitted light from the measured objects is separated into rays and received at the numerous unit photodetector having undergone the wavelength calibration in order to obtain the quality evaluation values of the measured objects. In other words, it is possible to reduce errors in wavelength for the photo-detective information for obtaining quality evaluation values of fruits and vegetables acting as measured objects.
In the conventional apparatus noted above, the calibration formula is established with the multiple regression analysis technique using the photo-detective data for all the elements of the photodetector of the array type including numerous elements (unit photodetectors) capable of detecting separated rays with a small resolution. However, it is required to execute a great number of calculations when the calibration formula is established using the multiple regression analysis technique. As a result, an enormous working time is disadvantageously required in establishing the calibration formula.
In order to reduce the working time required in establishing the calibration formula, it is conceivable to reduce the number of plural unit photodetectors to diminish the photo-detective information by decreasing the wavelength resolution when separated rays are received. However, such a proposed arrangement would decrease the wavelength resolution per se when separated rays are received at the plurality of unit photodetectors, even if the above-noted wavelength calibration process is properly executed to determine the wavelengths received at the unit photodetectors, respectively, based on the data received at each unit photodetector. As a result, there occurs a risk of lowering the measurement accuracy of the photo-detective information for obtaining the quality evaluation values of fruits and vegetables.    [Patent Document 1]
Japanese Patent Publication No. 2002-107294 (see pages 5 through 6, FIG. 5 and FIG. 6)    [Patent Document 2]
Japanese Patent Publication No. 2002-90301 (see pages 3 through 5, FIG. 1, FIG. 4 and FIG. 5)